This Month in your Garden – May

A month in three parts...

Let’s divide the month of May into three. It’s as busy a month as you want it to be with summer warmth coming and herbaceous plants putting on a growth spurt. It all depends on what you want to see in the garden in the coming months, in addition to your existing planting. 

If you favour dahlias then in early May you can plant tubers outdoors if you haven’t already started them in a greenhouse or frame. Cover them with about three inches (7cm) of soil to protect against late frost. Harden off bedding plants in frames, such as pelargoniums, marguerites and fuchsias, in fact most half-hardy annuals sown in late February should be hardened and ready for open ground by the end of the month. But keep an eye on the weather reports in case of frost. 

You will probably need to give dahlias, salvias and cannas grown in the greenhouse or frames a little longer because they are more susceptible to the cold. Give roses an early spraying to prevent blackspot and watch out for greenfly. As fast as plants are growing so are the weeds and if you’re planting up borders later in the month you need to get weeding. By mid May you should be clearing the ground and lifting spring bulbs. Don’t cut the leaves off daffodils, hyacinths and tulips, heel the bulbs into a trench, cover with soil and let them gain strength for another year. 

Plant out early flowering chrysanthemums, hardy perennials and alpines grown in a frame or greenhouse. By late May you can be planting out your hardened-off summer bedding and planting up containers, hanging baskets and window boxes with subtle summer shades or riots of colour from trailing lobelia, pelargoniums, fuchsias, petunias, campanula or whatever takes your fancy.   

• Mulch your borders to suppress weeds and keep the moisture in
• Feed young plants to encourage growth
• Tie in sweet peas and remove side shoots in late May
• Take softwood cuttings of shrubs and herbs
• Tidy early flowering Clematis
• Look out for signs of vine weevils in containers
• Feed lawns
• Pinch out growing tips of young plants
• Sow half-hardy annuals outdoors when the soil warms up
• Deadhead flowered rhododendrons and azaleas
• Shade the greenhouse and frames in hot weather.